Metallic materials are widely used in various electrochemical devices, including the electrode in a chlor-alkali process and the separator plates in fuel cells. Metal components are also used in batteries, electrolyzers and electrochemical gas separation devices. In most of these applications, the surface of the metal components need to have high electrical conductance (or low electrical resistance) to reduce the internal electrical losses of the electrochemical devices, or high activity for electrode reactions to reduce electrode polarization, for high operation efficiency. The major challenge for this application is that the metal component must also have high corrosion resistance while maintaining its high electrical conductance. In applications using metal as an electrode, the metal surface should have high catalytic activity for a highly efficient electrode reaction.
U.S. Pat. No. 6,649,031 discloses fuel cell metal bipolar plates that are coated with a corrosion resistant and electrically conductive carbon layer that with a sub-layer between the metal substrate and coating layer. In order to further improve the corrosion resistance, the coating layer is treated with an overcoating sealing that seals off the pores in the carbon layer.
U.S. Pat. No. 6,689,213 discloses a fuel cell metal bipolar plate that has a multi-phase surface coating. One phase is metal, and the other phase is a compound phase that consists of metal nitride, oxide, carbide or boride.
US patent application publication no. 2006/0134501 discloses a fuel cell metal separator plate that has an electrically conductive, corrosion resistant surface layer on a metal substrate. The surface layer comprises metal carbides, metal borides, and metal oxides. There is a metal layer between the surface layer and the metal substrate to improve the adhesion of the surface layer and the metal substrate. It has Cr-rich surface passive film.
US Patent application publication no. 2009/0269649 discloses a fuel cell stainless steel separator plate that has an electrically conductive and corrosion resistant surface layer that comprises metal nitride, carbide and metal boride. The surface layer is deposited on the surface modified stainless steel.
US Patent application publication no. 2008/0107928 discloses a fuel cell bipolar plate that has a gold (Au) or platinum (Pt) surface layer and an oxygen containing interface layer.
US Patent application publication no. 2009/0015029 discloses fuel cell bipolar plates that are coated with an electrically conductive layer. The conductive layer could be carbon, molybdenum doped indium oxide, chromium nitride or an MoSi2 layer. The '029 publication does not specifically disclose an underlayer between the conductive coating layer and the substrate layer.
US Patent application publication no. 2007/0003813 discloses using conductive oxide including doped TiO2 as a surface coating layer in fuel cells. The deposition process includes physical vapor deposition.
There remains a need for a method that produces metal components for electrochemical devices that need high electrical conductance, corrosion resistance and electrode reaction activities for long term operation at a low cost.